Sugar is a common carbohydrate sourced from sugar cane and sugar beet used in food because of its sweet taste. Ordinary table sugar (sucrose) is a disaccharide made up of one molecule of glucose bound by a α-1,2-glycoside to one molecule of fructose. Table sugar is 99.5% sucrose, the most biologically abundant disaccharide. Saccharides are simple carbohydrates classified as monosaccharides, oligosaccharides or polysaccharides depending upon their structure. Sucrose is sourced from both sugarcane and beets.
i) Sugar Processing
The processing steps required to produce white sugar result in generation of a number of byproducts, most of which are considering waste products with little or no nutritional value or use in human applications.
After being mechanically harvested, sugar cane is transported to a mill and crushed between serrated rollers. The crushed sugar cane is then pressed to extract the raw sugar juice, while the bagasse (leftover fibrous material) is used for fuel. The raw juice is then heated to its boiling point to extract any impurities and lime and bleaching agents are added and mill mud is removed. The raw juice is further heated under vacuum to produce bulk sugar crystals and a thick syrup known as molasses. The two are separated by a centrifuge and the molasses waste stream is collected for use as a low-grade animal feedstock. The bulk sugar crystals are further refined to increase their purity.
The bulk sugar crystals from the above process are further refined to produce the many commercially available sugar products. The bulk sugar crystals are mixed with a hot concentrated syrup to soften the outer coating on the crystals. The crystals are recovered by centrifuge and then dissolved in hot water. This sugar liquor is then further purified by carbonation or phosfloatation, filtration, decolourisation and then seeded with fine sugar crystals. Once the crystals have grown to the requisite size, the crystals are separated from the syrup by centrifuge, dried, graded and then packaged. There may be several repetitions of recovering sugar crystals from the sugar liquor. The dark sugar syrup which is left after all of the sugar crystals have been recovered is also called molasses.
Approximately 70% of the world's sugar comes from sugar cane and about 30% comes from sugar beets. Similar processes are used to manufacture sugar products from sugar beets. However, it is a single step rather than two step process.
The processing starts by slicing the beets into thin strips/chips/cossettes. This process increases the surface area of the beet to make it easier to extract the sugar. The extraction takes place in a diffuser where the beet is kept in contact with hot water and the resultant sugar solution is referred to as the juice. The exhausted beet slices from the diffuser are then pressed to squeeze as much juice as possible out of them. The pressed beet, by now a pulp, is sent to drying plant where it is turned into pellets which form an important constituent of some animal feeds. The juice is then cleaned up before it can be used for sugar production and the non-sugar chemicals are removed in a process called carbonation (milk of lime (calcium hydroxide) and carbon dioxide gas). The calcium carbonate (chalk) which forms traps the non-sugar chemicals and is removed (called mud) in the clarifier. Once this is done the sugar liquor is concentrated until sugar crystals form. Once the crystals have grown the resulting mixture of crystals and mother liquor is spun in centrifuges to separate the two. The crystals are then given a final dry with hot air before being packed and/or stored ready for dispatch. The final sugar is white and ready for use. Because one cannot get all the sugar out of the juice, there is a sweet by-product made: beet molasses. This is usually turned into a cattle food or is sent to a fermentation plant such as a distillery where alcohol is made.
ii) Polyphenols, Polyphenol Glycosides and Phenolic Acids
Polyphenols (compounds with two or more phenol groups) are a class of phytochemicals found in a variety of sources including wine, grapes, cocoa and sugar cane and sugar beet. Natural polyphenols can range from simple molecules such as phenolic acids to large highly polymerized compounds such as tannins. Polyphenols (or phenolics) all have a common basic chemical component, that is, a phenolic ring structure. There are at least 8000 identified polyphenols in a number of subcategories, such as anthocyanins and catechins. Polyphenols can exist in their free form, or as polyphenol glycosides.
Conjugated forms of polyphenols are the most common, where various sugar molecules, organic acids and lipids (fats) are linked with the phenolic ring structure. Despite having a common phenolic ring structure, differences in the conjugated chemical structure, size and other substituents account for different chemical classifications and significantly, variation in the modes of action and health properties of the various compounds.
Phenolic acids are simple molecules such as caffeic acid, vanillin, and coumaric acid. Phenolic acids form a diverse group that includes the widely distributed hydroxybenzoic and hydroxycinnamic acids (despite the latter two only having one phenolic ring). Hydroxycinnamic acid compounds (p-coumaric, caffeic acid, ferulic acid) occur most frequently as simple esters with hydroxy carboxylic acids or glucose, while the hydroxybenzoic acid compounds (p-hydroxybenzoic, gallic acid, ellagic acid) are present mainly in the form of glucosides. Coffee is particularly rich in bound phenolic acids, such as caffeic acid, ferulic acid, and p-coumaric acid.
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